Linker Optimization Enhances the Potency of Ribonuclease-Targeting Chimeras in Cancer Models

A ribonuclease-targeting chimera (RiboTAC) is a heterobifunctional compound that binds to an RNA target and recruits a ribonuclease to cleave the bound RNA. This study investigates the impact of linker length and composition on RiboTAC potency in leukemia and breast cancer cellular models. Increasing linker length from two polyethylene glycol units to eight increased RiboTAC potency, while longer linker lengths decreased potency. The optimized RiboTAC reduced the abundance of oncogenic LGALS1 transcripts in THP-1 leukemia cells (∼95%) and in MDA-MB-231 triple negative breast cancer cells (∼70%), leading to a subsequent decrease of galectin-1 protein and induction of apoptosis. A series of target engagement assays were developed to validate effector protein-small molecule engagement in vitro and in cells, demonstrating the broad potential of these assays to study recruitment of other effector proteins. Collectively, these findings underscore the importance of linker optimization for enhancing RiboTAC potency.